1. Field of Invention
The present invention relates to a polarization conversion element for converting an unpolarized light beam incident thereto into a predetermined polarized light beam, a method of producing the polarization conversion element, and a projector including the polarization conversion element.
2. Description of Related Art
A light-modulation element, which can be referred to as a light valve, is used in a projector in order to modulate a light beam in accordance with an image signal. A light valve of the type which uses only one type of linearly polarized light beam, such as a transmissive liquid crystal panel or a reflection liquid crystal panel, is often used. Accordingly, a projector, which uses one type of linearly polarized light beam, includes a polarization conversion element for converting an unpolarized light beam, which has exited a light source, into one type of linearly polarized light beam (such as an s-polarized light beam or a p-polarized light beam).
Examples of conventional polarization conversion elements are described in Japanese Unexamined Patent Application Publication No. 10-177151 and Japanese Unexamined Patent Application Publication No. 10-90520 disclosed by the Applicant.
A conventional polarization conversion element is produced, for example, by cutting out a polarization beam splitter array, making up the polarization conversion element from a composite plate formed by alternately bonding, with an adhesive, a transmissive plate having a polarization separation film and a reflection film formed thereon, and a transmissive plate which does not have anything formed thereon.
The step of bonding multiple transmissive members together takes a relatively long time to perform because it is ordinarily performed by repeatedly bonding the plates together with ultraviolet curing optical adhesive and curing the optical adhesive. In order to increase the efficiency with which the polarization conversion element is produced, there has been a desire to increase the efficiency with which the bonding step is performed.
The present invention overcomes the aforementioned conventional problem. An object of the invention is to provide a technology which makes it possible to produce a polarization conversion element with high efficiency.
To solve at least part of the aforementioned problem, a first producing method in accordance with the present invention is a method of producing a polarization conversion element that converts an unpolarized light beam incident thereto to a predetermined polarized light beam, the method comprising the steps of:
(a) providing a plurality of first transmissive plates;
(b) providing a plurality of second transmissive plates;
(c) forming a plurality of polarization separation films and a plurality of reflection films on surfaces of portions of the first transmissive plates or the second transmissive plates, so that the plurality of polarization separation films and the plurality of reflection films are alternately disposed on interfaces of the transmissive plates, when the plurality of first transmissive plates and the plurality of second transmissive plates are alternately disposed and bonded together;
(d) producing a composite plate, having the plurality of polarization separation films and the plurality of reflection films alternately disposed on each of the interfaces of each of the transmissive plates, as a result of alternately disposing and bonding together the plurality of first transmissive plates and the plurality of second transmissive plates; and
(e) producing a transmissive block having a light-incident surface and a light-exiting surface, formed parallel to cut surfaces formed by cutting the composite plate along cutting planes parallel to planes at a predetermined angle from planar surfaces of the composite plate;
wherein the step (d) includes the step of forming the polarization separation films so that a transmittance ratio of each polarization separation film, for an ultraviolet light beam of a particular wavelength region, incident on a surface of each polarization separation film at an angle of incidence of approximately 0 degrees, is approximately 40% or more.
According to the above-described first producing method, the transmittance ratio of each polarization separation film for an ultraviolet light beam can be increased, so that, in step (d), an optical adhesive used to bond the first transmissive plates and the second transmissive plates can be efficiently irradiated with ultraviolet light beams, making it possible to decrease the number of man-hours required to cure the adhesive. Therefore, the polarization conversion element can be produced with high efficiency.
It is preferable that the particular wavelength region lie in a range of 365 nmxc2x130 nm.
It is preferable that the step of forming the polarization separation films include the step of forming multilayered structural sections formed by alternately placing first and second layers upon each other, with a refractive index of each first layer being smaller than a refractive index of each transmissive member and a refractive index of each second layer being greater than the refractive index of each transmissive member; the refractive index of each transmissive member be approximately 1.48 to approximately 1.58; and the first layers of the polarization separation films each be formed of MgF2, and the second layers of the polarization separation films each be formed of MgO.
By forming the polarization separation films as described above, each polarization separation film can have a transmittance ratio for an ultraviolet light beam of a particular wavelength range of approximately 40% or more.
In the first producing method, it is preferable that the step (d) comprise the step of forming the reflection films so that a transmittance ratio of each reflection film for an ultraviolet light beam of a particular wavelength region incident to a surface of each reflection film at an angle of incidence of approximately 0 degrees is approximately 40% or more.
According to the foregoing description, the transmittance ratio of each reflection film for an ultraviolet light beam can be increased, so that, in step (d), the optical adhesive used to bond the first transmissive plates and the second transmissive plates together can even be more efficiently irradiated with ultraviolet light beams, making it possible to further decrease the number of man-hours required to cure the adhesive. Therefore, the polarization conversion element can be produced with even higher efficiency.
It is preferable that the particular wavelength region lie in a range of 365 nmxc2x130 nm.
It is preferable that the step of forming the reflection layers include the step of forming multilayered structural sections formed by alternately placing third and fourth layers upon each other, with a refractive index of each third layer being smaller than a refractive index of each transmissive member and a refractive index of each fourth layer being greater than the refractive index of each transmissive member; each transmissive member have a refractive index of approximately 1.48 to approximately 1.58; and the third layers of the reflection films each be formed of SiO2, and the fourth layers of the reflection films each be formed of TiO2 or Ta2O5.
By forming the reflection films as described above, the transmittance ratio of each reflection film for an ultraviolet beam in a particular wavelength region can be approximately 40% or more.
A second producing method in accordance with the present invention is a method of producing a polarization conversion element that converts an unpolarized light beam incident thereto to a predetermined polarized light beam, the method comprising the steps of:
(a) providing a plurality of first transmissive plates;
(b) providing a plurality of second transmissive plates;
(c) forming a plurality of polarization separation films and a plurality of reflection films on surfaces of portions of the first transmissive plates or the second transmissive plates, so that the plurality of polarization separation films and the plurality of reflection films are alternately disposed on interfaces of the transmissive plates, when the plurality of first transmissive plates and the plurality of second transmissive plates are alternately disposed and bonded together;
(d) producing a composite plate having the plurality of polarization separation films and the plurality of reflection films alternately disposed on each of the interfaces of each of the transmissive plates as a result of alternately disposing and bonding together the plurality of first transmissive plates and the plurality of second transmissive plates; and
(e) producing a transmissive block having a light-incident surface and a light-exiting surface, formed parallel to cut surfaces formed by cutting the composite plate along cutting planes parallel to planes at a predetermined angle from planar surfaces of the composite plate;
wherein the step (d) includes the step of forming the reflection films so that a transmittance ratio of each reflection film, for an ultraviolet light beam of a particular wavelength region, incident on a surface of each reflection film at an angle of incidence of approximately 0 degrees, is approximately 40% or more.
According to the second producing method, the transmittance ratio of each reflection film for an ultraviolet light beam can be made high, so that, in step (d), the optical adhesive used to bond the first transmissive plates and the second transmissive plates can be efficiently irradiated with ultraviolet light beams, making it possible to decrease the number of man-hours required to cure the adhesive. Therefore, the polarization conversion element can be produced with high efficiency.
A first polarization conversion element in accordance with the present invention comprises:
a plurality of transmissive members arranged along a predetermined direction; and
a plurality of polarization separation films and a plurality of reflection films alternately disposed between the plurality of transmissive members;
wherein a transmittance ratio of each polarization separation film for an ultraviolet light beam of a particular wavelength region, incident on a surface of each polarization separation film at an angle of incidence of approximately 0 degrees, is approximately 40% or more.
The above-described first polarization conversion element comprises polarization separation films each having a high transmittance ratio for an ultraviolet light beam of a particular wavelength region, so that the polarization conversion element can be produced with high efficiency.
It is preferable that, in the first polarization conversion element, a transmittance ratio of each reflection film for an ultraviolet light beam of a particular wavelength region incident to a surface of each reflection film at an angle of incidence of approximately 0 degrees be approximately 40% or more.
The first polarization conversion element comprises reflection films each having a high transmittance ratio for an ultraviolet light beam of a particular wavelength region, so that the polarization conversion element can be produced with even higher efficiency.
A second polarization conversion element in accordance with the present invention comprises:
a plurality of transmissive members arranged along a predetermined direction; and
a plurality of polarization separation films and a plurality of reflection films alternately disposed between the plurality of transmissive members;
wherein a transmittance ratio of each reflection film for an ultraviolet light beam of a particular wavelength region, incident to a surface of each reflection film at an angle of incidence of approximately 0 degrees, is approximately 40% or more.
The second polarization conversion element comprises refractive films each having a high transmittance ratio for an ultraviolet light beam of a particular wavelength region, so that the polarization conversion element can be produced with high efficiency.
A first projector in accordance with the present invention comprises:
a light source from where an unpolarized light beam exits;
a polarization conversion element that converts the light beam from the light source into a predetermined polarized light beam;
a light modulation device that modulates the light beam which exits from the polarization conversion element based on a provided image signal; and
a projection optical system that projects the light beam modulated by the light modulation device;
wherein the polarization conversion element comprises:
a plurality of transmissive members arranged along a predetermined direction; and
a plurality of polarization separation films and a plurality of reflection films alternately disposed between the plurality of transmissive members; and
wherein a transmittance ratio of each polarization separation film for an ultraviolet light beam of a particular wavelength region, incident on a surface of each polarization separation film at an angle of incidence of approximately 0 degrees is, approximately 40% or more.
The first projector comprises a first polarization conversion element of the present invention, so that the device can be produced with high efficiency.
A second projector in accordance with the present invention comprises:
a light source from where an unpolarized light beam exits;
a polarization conversion element that converts the light beam from the light source into a predetermined polarized light beam; and
a light modulation device that modulates the light beam which exits from the polarization conversion element based on a provided image signal; and
a projection optical system that projects the light beam modulated by the light modulation device;
wherein the polarization conversion element comprises:
a plurality of transmissive members arranged in a predetermined direction; and
a plurality of polarization separation films and a plurality of reflection films alternately disposed between the plurality of transmissive members; and
wherein a transmittance ratio of each reflection member for an ultraviolet light beam of a particular wavelength region, incident on a surface of each reflection film at an angle of incidence of approximately 0 degrees is, approximately 40% or more.
The above-described second projector comprises a second polarization conversion element of the present invention, so that the device can be produced with high efficiency.